FIG. 1 is a block diagram explaining conventional color-printer calibration.
An ink color-separation processor 901 performs color separation processing on input multilevel RGB image data by interpolation processing such as tetrahedral interpolation based on table information from an ink color-separation table 907, to obtain respective cyan (C), magenta (M), yellow (Y) and black (K) color component data corresponding to color materials of a color printer.
A calibration CMYK 1-dimensional look-up table (1D LUT) 902 is used for correction of tonality characteristic of image data in correspondence with color reproduction characteristics of the printer. The 1D LUT 902 is used for correcting the multilevel CMYK data outputted from the ink color-separation processor 901 to multilevel C′M′Y′K′ data. By this processing, calibration in correspondence with the characteristics of the color printer is realized.
A halftone processor 903 converts the multilevel C′M′Y′K′ data to data of tonality levels printable by the color printer. For example, if the color printer is a binary printer, the halftone processor 903 performs halftone processing on the C′M′Y′K′ data and outputs binary C″M″Y″K″ data.
A color printer engine 904 performs printing based on the input C″M″Y″K″ data.
A sensor 906 examines the color reproduction characteristics of the color printer engine 904. Based on the color reproduction characteristics of the respective CMYK colors outputted from the sensor 906, a 1-dimensional LUT generator 905 generates 1D LUTs for the respective CMYK colors so as to obtain target color reproduction characteristics, and writes the generated tables into the 1D LUT 902.
In the technique using the 1D LUT 902 as shown in FIG. 1, as the respective CMYK colors are independently calibrated, high-accuracy calibration can be realized as to primary colors. However, regarding colors other than primary colors including secondary colors such as red (R), green (G) and blue (B), tertiary colors, quaternary colors constituting a gray line, and the like, high-accuracy calibration cannot be realized.
Such secondary, tertiary and quaternary colors can be calibrated by reconstructing the contents of the ink color-separation table 907. However, it is difficult to reconstruct the ink color-separation table 907 within the limitation of total ink amount permissible for a print sheet.
Further, as a recent ink-jet printer employs a 6-color ink system using pale cyan and pale magenta inks in addition to cyan, magenta, yellow and black inks, it is more difficult to keep the construction within the above limitation.